I don't know what more information you are expecting.
The hypothesis the batteries would need to be changed every two weeks is based on the assumption she turns it off when she is done. Therein lies the problem (see OP), she does not turn it off, then falls a sleep and it is on for 4-16 hours per usage. I have purchased alkaline cells. The package of 36 costs $11.99 and was empty in three weeks (2 at a time). If they had made the unit so I didn't have to take it off the wall, I probably wouldn't have an issue.